Who will benefit

Nearly half a million Australians will be covered by the scheme when it is fully operational in 2019.

It is designed to offer people with permanent and significant disabilities the ability to choose what sort of care and support they need.

Disability campaigners say the scheme will improve lives.

"[The NDIS] changes their lifestyle from being a dependant lifestyle into one where they have all the sorts of opportunities that other Australians take for granted," said John Della Bosca, from the lobby group Every Australian Counts.

The scheme provides funding for therapeutic treatment, home and car modifications, equipment such as wheelchairs and walkers, as well in-home help.

"Whatever is reasonably necessary to for people to normalise their life, to have the life the rest of us take for granted," Mr Della Bosca said.

The NDIS will allow people more control over the services they receive.

Each person will be allocated a budget to manage themselves if they want to.

But with that independence comes uncertainty for some.

"For them that's the biggest change is understanding their responsibilities and commitment to managing their own money, which they've never had that responsibility, but with that comes extraordinary freedom," Elise Stumbles from the Cerebral Palsy Alliance said.

The rollout

The scheme is being launched at four sites across the country.

In New South Wales, the launch site is Newcastle, in the Hunter region.

According to DisabilityCare Australia, about 10,000 people in New South Wales will be covered by 2016.

By 2018, all 140,000 New South Wales residents with a disability will be covered.

Victoria's trial site is in the Barwon region, and it will expand to cover about 100,000 Victorians by mid-2019.

The South Australian launch focuses on early intervention for children aged up to five years.

NDIS: Key points

Begins July 1, 2013

Will cover more than 400,000 people by 2019

NSW, SA, Tasmania and Victoria will host launch sites

The ACT, NT and Queensland will come in line in coming years

WA has not signed up

It will help pay for carers, new wheelchairs, home modifications, physiotherapy and speech pathology

To be eligible, you must have a significant and permanent disability

People over 65 are unable to access the scheme

It will cost the Federal Government $19.3 billion over seven years

Around 5,000 children will take part in stage one of the scheme, which will be gradually expanded to cover the 33,000 South Australians living with a disability.

In Tasmania, the scheme will begin with support for 1,000 young people aged between 15 and 24 and expand to cover 11,000 people by July 2018.

The ACT and NT schemes begin in 2014, and Queensland in July 2016.

Western Australia is yet to sign up to the scheme.

Logistical problems

One problem the scheme will encounter as it expands is a lack of trained staff.

There are currently fewer than half the specialist disability care workers and therapists the scheme needs.

Mr Della Bosca says there is a real need to attract new people to the sector, and training them will be a big challenge.

"We know that first of all recruiting people is a tough task to any sector," he said.

"When you're talking about doubling its size in a relatively short period of time and then providing highly expert training to a large number of people, we don't have enough people to do the training as well.

"That's going to be a problem for a long time to come but I think it's one that's being tackled by government.

"It's being tackled by service providers and by people with a disability themselves."

Mental illness

About 10 per cent of Australians suffering mental illness will be covered by DisabilityCare Australia.

Frank Quinlan from the Mental Health Council of Australia says the system will provide people with mental illness with support when they need it most.

"They can receive intensive support," he said.

"At a time when they're not in need of much support that can be backed off, but it's sort of held ready to go again.

"So people will not have to continually reapply and exit the scheme. It can be can be ramped up and down according to particular needs."